Question: In math class, the girl to boy ratio is $5$ to $3$. If there are $15$ girls, how many boys are there?
Explanation: A ratio of $5$ girls to $3$ boys means that there is a group of $5$ girls for every group of $3$ boys. If there are $15$ girls, then there are $3$ groups of $5$ girls each. Because we know the ratio is $5:3$ , there must be $3$ groups of $3$ boys each. There is a total of $9$ boys in math class.